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Microstructural evolution and mechanical properties of alloy 718 fabricated by selective laser melting following different post-treatments

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Rare Metals 2021年第11期40卷 3222-3234页

作者： Hao Luo Xiao-Qiang Li Cun-Liang Pan Peng-Jiang He Ke-Li Zeng National Engineering Research Center of Near-Net-Shape Forming for Metallic Materials South China University of TechnologyGuangzhou 510640China Institute of Materials and Processing Guangdong Academy of SciencesGuangzhou 510650China Dongguan Hyperpowder Co.Ltd. Dongguan 523808China

In this study,alloy 718 specimens were fabricated via selective laser melting(SLM),and the effects of different post-treatments on microstructures and mechanical properties of the alloy were systematically *** post-treatment techniques investigated were solid solution+dual aging(SA) and hot isostatic pressing+solid solution+dual aging treatment(HIP+SA).The results indicate that the specimens treated using SA have a columnar crystal structure similar to the as-built sample,the microstructure is partially recrystallized,and the grain size increases ***,the grain morphology is dominated by equiaxed crystals in samples treated using HIP+SA,and the microstructure is completely recrystallized,with distinct grain coarsening and a large number of twins *** treated using SA and HIP+SA show high tensile strength and yield strength and excellent elongation at room temperature,which can be primarily attributed to the strengthening of the γ’ and γ "precipitated *** number of γ" precipitated phases are reduced due to the consumption of Nb to form a large amounts of δ phase and(Ti,Nb)C carbides,resulting in the strength of HIP+SA specimens being lower than that of SA specimens.

关键词： Selective laser melting alloy 718 Post-treatments Microstructural evolution Mechanical properties

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Investigation of secondary phases and tensile strength of nitrogen-containing alloy 718 weldment

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International Journal of Minerals,Metallurgy and Materials 2020年第9期27卷 1259-1268页

作者： Behrooz Nabavi Massoud Goodarzi Abdul Khaliq Khan School of Metallurgy and Materials Engineering Iran University of Science and TechnologyTehran ***Iran Department of Mechanical Engineering Manitoba Institute for MaterialsUniversity of ManitobaWinnipeg R3T 2N2Canada

The influence of nitrogen content on the precipitation of secondary phases and the tensile strength of alloy 718 during gas tungstenarc welding was investigated. Various types of precipitates were characterized using scanning electron microscopy and transmission electronmicroscopy. The results showed that in the fusion zone, the volume fraction of Nb-rich phases such as Laves, (Nb,Ti)C, and δ phases, as wellas Ti-rich phases such as (Ti,Nb)CN and (Ti,Nb)N, increased with increase in the nitrogen content due to the microsegregation of Nb and Tiwithin interdendritic areas. Nitrogen was also found to decrease the size of γ′′ particles within γ dendrites. For precipitates in the partiallymelted zone, constitutional liquation was observed for both (Nb,Ti)C and (Ti,Nb)N particles. Based on the results of tensile tests, the weld containing0.015wt% nitrogen exhibited the highest ultimate tensile strength (UTS), whereas more addition of nitrogen led to a decrease in both theUTS and yield strength due to the increased content of brittle Laves phases and decreased size of γ′′.

关键词： nitrogen secondary phases gas tungsten arc welding tensile strength alloy 718

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维普期刊数据库

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CREEP CRACK GROWTH BEHAVIOR OF alloy 718 DURING HIGH TEMPERATURE EXPOSURE

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Acta Metallurgica Sinica(English Letters) 2005年第2期18卷 164-172页

作者： J.X.Dong M.C.Zhang Y.P.Zeng X.S.Xie DepartmentofMaterialScience UniversityofScienceandTechnologyBeijingBeijing100083China

alloy 718 is a precipitation strengthened nickel-based superalloy based on the precipitation of γ″-Ni3Nb (DO22 structure) and γ′-Ni3(Al,Ti) (L12 structure) phases. Creep crack growth rate (CCGR) was investigated after high temperature exposure at 593, 650 and 677℃ for 2000h in alloy 718. In addition to the coalescence of γ′/ γ″ and the amount increasing of δ phase, the existence of a bcc chromium enriched α-Cr phase was observed by SEM, and the weight fraction of α-Cr and other phases were determined by chemical phase analysis methods. The CCGR behavior and regulation have been analyzed by means of strength and structure analysis approaches. The experimental results show higher the exposure temperature and longer the exposure time, lower the CCGR. This is probably attributed to the interaction of material softening and brittling due to complex structure changes during high temperature exposure. Therefore, despite α-Cr phase formation and amount enhancement were run in this test range. It seems to us a small amount of α-Cr will be not harmful for creep crack propagation resistance, which is critical for disk application in aircraft and land-based gas turbine.

关键词： alloy 718 creep crack growth rate α-Cr phase

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